On-treatment PLAtelet reactivity-guided Therapy modification FOR ST-segment elevation Myocardial infarction (PLATFORM) is an investigator-initiated, prospective, randomized, parallel-group, controlled clinical trial designed to test the hypothesis that antiplatelet therapy modification is superior to standard antiplatelet regimen among intermediate to high-risk STEMI patients undergoing PPCI. The safety hypothesis is that compared with control arm, interventional study arm will have similar rates of non-coronary artery bypass graft surgery-related bleeding. Approximately 632 ST-elevation myocardial infarction (STEMI) patients with intermediate to high-risk (RISK-PCI score >3) clinical features undergoing PPCI will be randomly allocated to treatment modification or standard treatment. Low responders to aspirin will receive 200 mg aspirin for 30 days. Low responders to clopidogrel will receive 180 mg ticagrelor for 1 year. Patients will be followed up to 1 year after PPCI.